in fish linked to heart attacks
of fish andfish oil (which contain omega three fatty acids) has
long been hypo- thesised to prevent heart attacks. A significant
number of Sri Lankan doctors recommend intake of fish oil
capsules with a view to prevent heart attacks and fish is a part
of Mediterranean diet which is believed to reduce the incidence
of heart attacks. Fish oils are prescribed by some Sri Lankan
doctors for the management of hypertri -glyceridaemia (high
serum levels of triglycerides) which is a risk factor for heart
has been suggested that long term exposure to low levels of mercury
predisposes to atherosclerosis by promoting the production of free
radicals or by inactivating several antioxidant mechanisms (Clarkson,
Toxicology of Mercury 1997). Mercury may bind to selenium to form
mercury selenide which is insoluble thus neutralising the beneficial
effect of selenium in prevention of atherosclerosis. Mercury may
neutralise the antioxidant properties of glutathione catalase and
super-oxide. Mercury may induce lipid peroxidation and mercury levels
are a strong predictor of oxidised low density lipoprotein in the
Kuopio Ischaemic Heart Disease Study. Mercury may promote platelet
aggregability and blood coagulability. It has been suggested that
mercury in fish may counteract the beneficial cardiovascular effects
of omega three fatty acids in fish.
scientific report in 1995 revealed an increased risk of heart attacks
among residents of Kuopio in Finland. It is noteworthy that there is a
very high consumption of fish in people of Finland.
is a highly reactive heavy metal and exposure to toxic levels of
mercury results in damage to the nervous system and kidneys. Fish
intake is a major source of exposure to mercury mainly in the form of
exisits in three forms (a) element mercury (b) inorganic mercury
compounds and (c) organic mercury, primarily methyl mercury. Exposure
to inorganic mercury occurs occupationally. People can also be exposed
to inorganic mercury from silver mercury dental fillings.
to methyl mercury results exlusively from the consumption of fish,
shellfish (prawns, crabs and lobsters) and marine animals. These foods
are a major source of mercury for the general population. Large fish
such as sharks and sword fish have very high concentrations of mercury
(around 1 mgm per gram), tuna, trout, pike and bass have intermediate
concentrations (0.1 to 0.5 mgm per gram) and most shellfish have lower
rates of heart attacks were found among mercury exposed workers (Barrigard
et al, Br. J. Ind. Med, 1990, 47, 99-104). Mercury levels were quite
high in Spanish heart patients and Spanish have a very high
consumption of fish.
us Food and Drug Administration (March 2001) advised pregnant women
and women who may become pregnant not to eat sword
fish, king mackeral and shark.
toe-nail mercury level was directly associated with risk of heart
attacks and the adipose tissue D. H. A. levels were inversely
associated with the risk of heart attacks. Therefore high mercury
content of fish may diminish the cardio protective effect of fish oil.
The authors in the above study do not advise people to avoid fish.
far as I am aware, the mercury levels of Sri Lankan heart patients
have not yet been studied. As there is a significant proportion of Sri
Lankan heart attack patients who don't have known risk factors such as
smoking, hypertension hyperlipidaemia (high serum LDL cholesterol,
high serum triglycerides low HDL levels etc), diabetes, obesity and
lack of exercise, it may be worthwhile for our researchers to measure
mercury levels in our heart attack patients and compare with a control
group without heart disease.
Dr. D. P. Atukorale